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Moon on the Move

StarDate:

August 15, 2017

The Moon will pass by several prominent companions over the next week. Tomorrow, the bright star Aldebaran, the eye of the bull, will stand just above the Moon at first light. On Friday and Saturday, the Moon will pass by the planet Venus, the “morning star.” And it’ll end its week of companionship on Monday, when it lines up with the Sun — creating a total solar eclipse.

Over the centuries, eclipses have helped astronomers learn a lot about the Sun and the universe. During an eclipse in 1868, for example, French and British astronomers discovered a new element in the Sun’s atmosphere. It was named “helium” for Helios, an ancient Greek Sun god. Later observations revealed that it’s the second-most-abundant element in the universe, after hydrogen.

Perhaps the most famous eclipse discovery came in 1919.

Just a few years earlier, Albert Einstein had published his theory of gravity, known as general relativity. Among other things, it predicted that the gravity of a massive object like the Sun would “warp” the space around it.

To test that idea, British astronomer Arthur Eddington led an expedition to an island off the coast of Africa. His team photographed the eclipse, as well as stars that appeared near the Sun in the darkened sky. The apparent positions of those stars were shifted a tiny bit by the Sun’s gravity — confirming general relativity, and turning Einstein into an international celebrity.

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